A class of 4-phenylamino-piperadines with strong analgesic activity is disclosed in French Pat. No. M 2430 (C.A. 62, 14634), and U.S. Pat. No. 3,141,823 discloses an analgesic and tranquilizing composition containing one particular compound of that class, namely N-(1-phenethyl-4-piperidyl)-propionanilide (generic name: Fentanyl), on combination with droperidol. However, fentanyl, being a very strong morphine-like analgesic, has a very substantial addition potential.